The present invention relates to an apparatus called a board turner, typically used in the manufacture of different composite boards such as plywood or particle boards. These manufacturing processes give rise to a need for turning a board around so that the upper side becomes the lower side of the board. This requirement appears, e.g., in the grading inspection of the boards.
To this end, there is used an apparatus comprising two conveyors and a board turner placed therebetween. One of the conveyors acts as an importing conveyor, i.e. infeed conveyor of the board to be turned, while the other conveyor performs as an exporting conveyor, i.e. outfeed conveyor of the turned board. The board turner is comprised of turning arms or fingers that are mounted on a common rotary shaft into lined groups forming an assembly later called a finger turnstile. The fingers of each lined group in the finger turnstile are mounted in the same plane passing through the center of rotary shaft of the finger turnstile. A conventional construction of the finger turnstile is provided with four sets of fingers in a 90xc2x0 angular disposition in respect to each other about the shaft. The finger turnstile is configured into an integrated assembly that can be rotated about its center axis by means of an electric or hydraulic motor.
A drawback of this construction is that its degree of freedom in regard to its rotation is extremely constrained at the instant a board is being transferred into a slot of the finger turnstile and, respectively, at the instant of board removal from a slot of the finger turnstile onto the outfeed conveyor. In practice, the finger turnstile must be kept stopped during either of these operations. A solution to this problem has been sought from synchronized operation of the board feed/removal motions with the rotational motion of the finger turnstile by means of different speed control arrangements. However, such systems have become complicated and, hence, the operating speed of the system has remained slow in spite of these efforts.
Now, a substantial improvement to the operating speed of a board turner apparatus system has been achieved by way of altering the basic construction of one fundamental member of the system, namely, the finger turnstile.
The present construction makes it possible to achieve an operating sequence, wherein the board to be turned around is delivered from the rising portion of the turning motion by means of one finger set to another finger set that is waiting on the descending portion of the turning motion, by means of a short angular movement passing through the vertical top-dead position. This kind of motion can be accomplished by way of adapting the receipt of a board falling onto the descending side of the finger turnstile to take place by means of a finger set that has been driven into a position slightly past the vertical top-dead position so as to be therein ready for the receipt of the board or, alternatively, is at least in a motion toward this position. The angular movement required from the finger set to pass over the vertical top-dead position is small and, while the finger sets are still in this position, the conveyors of the system may operate without any wait states so as to keep on importing a new board to the fetch area of the board turner and, respectively, exporting a previously turned and lowered board off from the outfeed area of the turner.